Direct writing cathode ray tube using a fan shaped beam



Jan. 5, 1965 N. F. FYLER 3,154,733

nmac'r WRITING cmzonz RAY TUBE usmc A FAN SHAPED BEAM Filed July 20. 1960 United States Patent 3,164,738 DIRECT WRITING CATHODE RAY TUBE USHNG A FAN SHAPED BEAM Norman F. Fyler, Menlo Park, Calif, assignor to Litton Industries of California, Beverly Hills, Calif. Filed July 20, 1966), Ser. No. 44,206 Claims. (Cl. 313-73) The present invention relates to a high speed cathoderay direct writing tube and more particularly to a high speed cathode-ray direct writing tube for producing an electron beam having a linear transverse cross-section and a predetermined electron density.

In many modern high speed electronic systems, and especially in the computer and communication fields, there is a constant need for high speed visual display of intelligence information. While many mechanical and electro-mechanical printing devices have been utilized to produce visual intelligible display, all of these devices have substantial inherent inertia which severely limits the speed of operation of the devices.

In order to avoid the foregoing described speed limitations inherent in the mechanical and electro-mechanical types of printing devices, there has been developed in the prior art a specialized type of cathode-ray tube called a direct writing tube which is similar to a conventional cathode-ray tube except that the phosphor screen is replaced with a face plate having a plurality of conducting wires embedded therein traversing the face of the tube from one side to the other. The face plate operates to permit a coded electron beam to be converted directly to a charge pattern which can be deposited through the conducting wires onto a record medium moving past the exterior side of the face plate. A backing plate maintained at ground potential is positioned contiguous with the remote side of the record medium and adjacent the face plate of the tube in order to maintain a uniform potential behind the record medium so that the charge pattern deposited thereon in response to the charged conductors corresponds in configuration and magnitude to the charge pattern ad magnitudes on the individual conductors. The charged portions of the record medium may then be developed by dusting the medium with black powder which electrostatically adheres to the charged areas, and fixing the powder to permanently adhere to the medium.

In the past, direct Writing cathode-ray tubes have been mechanized to produce electron beams having crosssections which are generally circular or elliptical, these types of beams often being referred to as pencil beams. In one of the most common and easily mechanized types of direct writing tubes a single row of wire conductors traverses the face plate and theelectron beam scans the row while the record medium moves continuously past the row, information being written on the medium as it passes the row of conductors. More particularly, the modulated or coded electron beam scans the row of conductors selectively chargng the conductors whereby the information to be recorded is placed on the record medium as it moves past the exterior ends of the row of conductors by inducing charged spots on the areas of the medium adjacent the ends of the charged conductors.

In mechanizing the foregoing type of direct Writing tube, it has been found desirable to limit the size of the electron beam so that it is smaller than the spacing between conductors thereby improving resolution for a given wire spacing by preventing charge deposition on two conductors at once. For example, if the conductors are spaced 4 mils apart, the electron beam should be less than 4 mils in diameter. When it is realized that conductors having diameters of from 1 to 2 mils are generally used it is apparent that a beam of less than 4 mils ice can vary a maximum of less than two mils from concentric alignment with each conductor without effecting the operation of the tube. Hence, the operation of the tube is limited by the accuracy with which each conductor can be positioned on the tube face and with which the point of contact of the electron beam with the face plate can be controlled. For example, if 2 mils diameter conductors are used, a combined displacement of 2 mils resulting from either variation from linear positioning of the centers of the wire conductors or fluctuations in beam positioning cause the beam to scan only a portion of the ends of the wires. Hence, distortion is introduced in the writing operation. Furthermore, if the fluctuations in the beam control circuity or in the positioning of the conductors is substantial, portions of the information to be printed may not be recorded at all.

The present invention overcomes the foregoing and other limitations of prior art direct writing cathode-ray tubes by providing a high speed direct writing cathode-ray tube which employs an electron beam having a linear transverse cross-section oriented normal to the row of wire conductors embedded in the tube face plate whereby the electron beam scans the total end areas of each and every conductor regardless of the inaccuracies with which the wire conductors are positioned in the face plate and regardless of the fluctuations experienced by the electron beam due to inaccurate electron beam control. In accordance with one of the basic concepts of the present invention, a cathode-ray direct writing tube electron beam is generated which has a linear transverse crosssection and a predetermined electron density which determines the writing speed of the tube.

In one embodiment of the invention a fan-shaped electron beam having a rectangular transverse crosssection with a pair of elongated parallel sides is produced by an electron beam generator and is swept back and forth in a direction normal to the pair of elongated sides by a pair of electrostatic deflection plates so that the beam scans a row of wire conductors embedded in a face plate of the tube, the beam being oriented with the elongated sides orthogonal to the row of conductors whereby a portion of the rectangular cross-section of the beam strikes the conductors in sequence regardless of fluctuations in beam positionng or in the positioning of the wire conductors. In the conventional manner, a recording medium is continuously moved adjacent the wire conductors and a backing plate maintained at ground potential is positioned contiguous the remote side of the recording medium and adjacent the face plate of the tube so that a uniform potential is maintained behind the record medium whereby a charge is deposited on the record medium which corresponds to the magnitude of the charge deposited on each conductor by the modulated electron beam.

It is therefore an object of the present invention to provide a direct writing cathode-ray tube system which overcomes the elfects of inaccuracies in the positioning of an array of wire conductors and in fluctuations in position of an electron beam.

It is another object of the present invention to provide a direct writing cathode-ray tube system producing an electron beam having a linear transverse cross-section.

It is still another object of the present invention to provide a direct writing cathode-ray tube system producing an electron beam having a rectangular transverse cross-section and a predetermined electron density.

It is still a further object of the present invention to provide a cathode-ray writing tube system producing a fan-shaped electron beam having a predetermined density, the predetermined density permitting the system to write at a preselected speed.

The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with fruther objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawing in which one embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

FIGURE 1 is an isometric view, partly in section, of a high speed cathode-ray direct writing tube in accordance with the invention;

FIGURE 2 is a diagrammatic side elevational view of the cathode-ray writing tube of FIGURE 1;

FIGURE 3 is a cross-sectional view of a pair of magnetic deflectors taken along line AA of FIGURE 2; and

FIGURE 4 is a fragmentary view of a face plate of the direct writing cathode-ray tube shown in FIGURE 1.

Referring now to the drawings wherein like or corresponding parts are designated by the same reference character throughout the several views, there is shown in FIGURE 1 an isometric View, partly in section, of a high speed direct writing cathode-ray tube system wherein a fan-shaped electron beam I1 generated by an electron beam generator I3 and a pair of fanning magnets 15 is deflected by a pair of deflection plates 17 to scan an array or row of wire conductors or electrodes 19 embedded in a face plate 21 affixed to the front of the tube envelope. As is further shown in FIGURE 1, an electrostatic record medium 23 is continuously moved along the exterior ends of the wire conductors whereby a charge is selectively deposited on the record medium in accordance with the modulated electron beam II. A backing plate 25 maintained at ground potential is positioned contiguous with the remote side of the record medium and adjacent face plate 21 for maintaining a uniform potential behind the record medium so that the charge deposited thereon in response to each charged wire conductor corresponds to the magnitude of the charge on each conductor.

Examining the fan-shaped electron beam 11, it is apparent that the transverse cross-section of the beam at the face plate is rectangular in shape and has a pair of elongated sides oriented normal to the row of conductors. Furthermore, it is clear that in contrast to the prior art pencil-shaped beam, only a portion of the cross-sectional area of the beam contacts the surface of the wire conductors so that only a portion of the electron beam contributes to developing a charge on the conductors. Since the writing speed of the system is dependent on the rate of charge deposited, the intensity or electron density of the beam before fanning should be increased so that the density after fanning is suflicient to maintain a sufliciently rapid rate of charge deposit.

Referring now with particularity to the generation of the fan-shaped beam I1, attention is directed to FIGURE 2 wherein there is shown a diagrammatic side view of the cathode-ray tube of the invention. As shown in FIG- URE 2, the electrons comprising the beam are emitted from a cathode 27 and are accelerated toward the face plate of the tube by an annular accelerating electrode 29 whereby a cylindrical shape or pencil beam is produced. As is further shown in FIGURE 2, as the pencil beam passes between a pair of fanning electromagnets 31, the magnetic field produced thereby reacts with the electrons in the beam to fan the beam out whereby the beams develop a rectangular transverse cross-section having a pair of substantially parallel elongated sides oriented normal to the row of conductors and of sufficient length at the face plate to overcome any variation in the positioning of the wire conductors from straight line form or any fluctuation in the beam position itself so that the beam remains in registry with the conductors.

Referring to fanning magnets 31 with more particularity, attention is directed to FIGURE 3 wherein there is shown a front view of the magnets taken along a line A-A of FIGURE 2. As is indicated in FIGURE 3, magnets 31 are so shaped that the magnetic field generated by the magnets intercepts the path of the electron beam normal to the direction of motion of the beam as well as to the direction in which it is desired to pull the beam so that the beam will have a rectangular transverse crosssection. As is dictated by the familiar right hand rule of physics, the electrons comprising beam 11 will be accelerated or deflected along a direction which is normal to the direction of movement of the electron beam as well as to the magnetic lines of force being cut by the beam so that the beam is distorted or elongated in the desired manner as shown in FIGURE 3. Thus, the beam takes on a rectangular transverse cross-section.

Furthermore, since the electrons have imparted thereto a velocity tending to elongate the beam, the electrons will continue to move outwardly even after they have left the immediate area of the fanning magnets. Hence, the beam continues to elongate or fan out after it has left the area adjacent magnets 31, and beam 11 therefore takes the fan-shape form shown in FIGURES 1 and 2. It is clear of course, that the actual magnitude of the elongated sides of the fan-shaped beam at the face plate is dependent upon the intensity of the magnetic field developed by magnets 31 as well as the distance between the face plate and magnets 31.

Referring now with particularity to the relative dimensions of the sides of the transverse cross-section of the electron beam at the face plate, attention is directed to FIGURE 4. There is shown in FIGURE 4, a fragmentary front View of face plate 21 and beam 11. As indicated in FIGURE 4, conductors 19 have a diameter desig nated as d while the center-to-center spacing between conductors is designated x. Furthermore, the width of the rectangular transverse cross-section of beam 11 at the face plate is designated a while the elongated side of the cross-section is designated [2.

In accordance with the present invention, width a should not be greater than (xd) since if the beam were any Wider the beam would contact two conductors concurrently. On the other hand, width a should not be less than d, otherwise, the beam would be unable to contact simultaneously the total cross-sectional end area of each conductor. In connection with the length b of the elongated sides of the electron beam, the length of the sides is not critical. For example, beams with b equal to 10 to 40 times a have been found to operate quite satisfactorily, the main point to remember in determining the length of the elongated sides of the beam is to make the sides sufliciently long to overcome the fluctuations in conductor positioning and beam positioning.

Continuing with the discussion of the invention, it should be noted that in FIGURE 2 the front interior surface of the tube envelope is plated with a conductive metallic layer 32 which is positioned on either side of the row of wire conductors. While the cathode-ray writing tube of the invention functions satisfactorily without this metallic layer, it has been found desirable to use such a metallic layer since it protects the portions of the tube envelope near the wires from being bombarded by the electron beam. Since the metallic layer is conductive, the electrons deposited thereon can be easily removed from the layer by connecting the layer to a source of ground potential thereby preventing an excessive charge build up on the layer.

It should be apparent that numerous modifications and alterations may be made in the embodiment of the invention herein described without departing from the invention. For example, beam 11 need not be fanshaped in order to obtain the advantages of the present invention. In this regard, it is clear that beam 11 could be a sheet or rectangular beam since these shapes as well as a number of others provide an elongated or linear transverse cross-section.

In addition, it should be noted that the ends of the wire conductors positioned within the tube envelope can be made flush with the face plate wall rather than project out from the face plate as is shown in FIGURE 2. However, the projected ends reduce the probability that the secondary emission electrons emitted by one of the wire conductors will strike the neighboring or surrounding wire conductors.

Furthermore, projecting the interior ends of the wire conductors out from the face plate permits a much higher percentage of the electron beam to impinge upon the wire conductors rather than on the surrounding insulating medium. In addition, the cross-sectional area of the interior ends of the wire conductors can be increased by fiaring the conductors outwardly in the vicinity of the interior end, as is shown in FIGURE 2. If the crosssectional end areas of the conductors are so increased the percentage of the electron beam intercepted by the wire conductors can also be increased resulting in an increased writing speed capability.

It should be noted that as shown in FIGURE 2 the external ends of the conductors are flared outwardly in the same manner as the internal ends whereby the electrostatic field configuration extends out axially a substantial distance from the end of the conductors while penetrating radially only minor distances. Hence, a charge is deposited upon the moving record medium in accordance with the charges on the wire conductors regardless of the fact that the paper is not in direct contract with the conductors. Accordingly, it is to be expressly understood that the scope of the invention is to be limited only to the scope of the appended claims.

What is claimed as new is:

l. A cathode-ray writing system for printing information on a dieletcric recording material, said combination comprising: an evacuated envelope including a base plate at one end having a row of conductors therein, each of said conductors having a diameter substantially equal to a first predetermined dimension and the spacing between adjacent ones of said conductors being substantially equal to a second predetermined dimension, each of said conductors having an exterior end outside said envelope and an interior end within said envelope; a cathode positioned within said envelope opposite said base plate and operable for generating a pencil shaped electron beam; shaping apparatus for operating upon the electrons in said beam to rearrange the electrons so that said beam has a substantially rectangular transverse cross-section with a first pair of parallel sides substantially normal to said row of conductors, and a second pair of parallel sides substantially parallel to said row of conductors, said first pair of parallel sides being substantially longer than said first predetermined dimension so that said electron beam covers said interior end of each of said conductors regardless of conductor misalignment, said second pair of parallel sides being shorter than said second predetermined dimension so that said electron beam strikes only one of said conductors in said row of conductors at a time and a deflecting means positioned within said envelope intermediate said shaping apparatus and said base plate for deflecting said electron beam in a direction substantially normal to said first pair of sides to selectively strike said conductors.

2. In a direct writing cathode-ray tube system, the combination comprising: an evacuated envelope having a face plate at one end; a row of wire electrodes extending through said face plate of said envelope; the diameter of each of said wire electrodes being a first predetermined dimension and the spacing between adjacent ones of said wire electrodes being a second predetermined dimension; an electron gun positioned in said envelope at the other end and operable for generating a modulated fan-shaped electron beam oriented substantially normal to said row of wire electrodes; the cross sectional dimension of said fan-shaped electron beam normal to said wire electrodes being substantially greater than said first predetermined dimension and the cross sectional dimension of said fanshaped electron beam parallel to said row of Wire electrodes being less than said second predetermined dimen sion and deflection means positioned intermediate said electron gun and said face plate for selectively deflecting said fan-shaped electron beam to cause said fanshaped beam to selectively sweep across the ends of said wire electrodes.

3. The combination defined in claim 2 wherein said face plate further includes an insulating media having a relatively low dielectric constant, said insulating media having said wire electrodes passing therethrough, said wire electrodes being of suflicient length for the inner ends of said wire electrodes to project into the interior of said envelope a preselected distance from said insulating media and the outer ends of said wire electrodes to project a preselected distance beyond the exterior surface of said face plate.

4. The combination defined in claim 3 wherein each of said wire electrodes fiare outwardly in the vicinity of their interior ends to increase the cross-sectional area of the interior ends of said electrodes.

5. The combination defined in claim 4 wherein said wire conductors flare outwardly in the vicinity of their exterior ends to increase the total cross-sectional area of their exterior ends.

References Cited in the file of this patent UNITED STATES PATENTS 1,985,093 Hehlgans Dec. 18, 1934 2,257,795 Gray Oct. 7, 1941 2,291,476 Kernkamp July 28, 1942 2,501,791 Silverman Mar. 28, 1950 2,698,399 Orr et al Dec. 28, 1954 2,952,796 Crews Sept. 13, 1960 FOREIGN PATENTS 946,727 Germany Aug. 2, 1956 

1. A CATHODE-RAY WRITING SYSTEM FOR PRINTING INFORMATION ON A DIELECTRIC RECORDING MATERIAL, SAID COMBINATION COMPRISING: AN EVACUATED ENVELOPE INCLUDING A BASE PLATE AT ONE END HAVING A ROW OF CONDUCTORS THEREIN, EACH OF SAID CONDUCTORS HAVING A DIAMETER SUBSTANTIALLY EQUAL TO A FIRST PREDETERMINED DIMENSION AND THE SPACING BETWEEN ADJACENT ONES OF SAID CONDUCTORS BEING SUBSTANTIALLY EQUAL TO A SECOND PREDETERMINED DIMENSION, EACH OF SAID CONDUCTORS HAVING AN EXTERIOR END OUTSIDE SAID ENVELOPE AND AN INTERIOR END WITHIN SAID ENVELOPE; A CATHODE POSITIONED WITHIN SAID ENVELOPE OPPOSITE SAID BASE PLATE AND OPERABLE FOR GENERATING A PENCIL SHAPED ELECTRON BEAM; SHAPING APPARATUS FOR OPERATING UPON THE ELECTRONS IN SAID BEAM TO REARRANGE THE ELECTRONS SO THAT SAID BEAM HAS A SUBSTANTIALLY RECTANGULAR TRANSVERSE CROSS-SECTION WITH A FIRST PAIR OF PARALLEL SIDES SUBSTANTIALLY NORMAL TO SAID ROW OF CONDUCTORS, AND A SECOND PAIR OF PARALLEL SIDES SUBSTANTIALLY TO SAID ROW OF CONDUCTORS, SAID FIRST PAIR OF PARALLEL SIDES BEING SUBSTANTIALLY LONGER THAN SAID FIRST PREDETERMINED DIMENSION SO THAT SAID ELECTRON BEAM COVERS SAID INTERIOR END OF EACH OF SAID CONDUCTORS REGARDLESS OF CONDUCTOR MISALIGNMENT, SAID SECOND PAIR OF PARALLEL SIDES BEING SHORTER THAN SAID SECOND PREDETERMINED DIMENSION SO THAT SAID ELECTRON BEAM STRIKES ONLY ONE OF SAID CONDUCTORS IN SAID ROW OF CONDUCTORS AT A TIME AND A DEFLECTING MEANS POSITIONED WITHIN SAID ENVELOPE INTERMEDIATEW SAID SHAPING APPARATUS AND SAID BASE PLATE FOR DEFLECTING SAID ELECTRON BEAM IN A DIRECTION SUBSTANTIALLY NORMAL TO SAID FIRST PAIR OF SIDES TO SELECTIVELY STRIKE SAID CONDUCTORS. 